The incidences of various allergic diseases, including asthma, pollinosis, food allergies, and allergic dermatitis, have recently been increasing; amid this situation, along with air pollution, stress and the like, there is a strong demand for the elucidation of the causes of these diseases and fundamental treatments. Mycobacterium bovis bacillus Calmette-Guerin (BCG) is an attenuated live vaccine that has been widely used as a tuberculosis vaccine all over the world for 80 years or more, and is known to suppress the onset of tuberculosis. From this fact, it is publicly known that the BCG live vaccine potently activates anti-tuberculosis immunity, that is, Th1 (cellular) immunoreactions. However, it remains unclear which component of BCG cell bodies and how it stimulates Th1 immunity to exhibit its prophylactic effect. For human applications, it is better to use an isolated cell body component with greater emphasis on safety. Although an extremely large number of therapeutic agents for allergic diseases, including steroid preparations, are available, many of them are symptomatic agents, with almost no pharmaceuticals known to be capable of preventing/treating allergic diseases by enhancing Th1 immunoreactions or suppressing Th2 immunoreactions.
Lipoarabinomannan (LAM) is a major component of the cell wall, and is thought to be a modulin that mediates a broad range of forms of immune control that are favorable for the survival of mycobacteria in infected hosts and anti-inflammatory effects. These effects include the suppression of T lymphocyte growth via antigen processing interruption (non-patent reference 1), inhibition of macrophage activation by interferon γ (non-patent reference 2), scavenging of oxygen-derived free radicals, and the like can be mentioned. LAM is not only a pathogenic factor that is responsible for macrophage inactivation, but also is involved in phagocytosis of mycobacteria in phagocytes (non-patent reference 3). Additionally, it has recently been proposed that phosphatidyl inositol mannosides (PIMs), which are thought to be precursors for lipomannan (LM) and LAM, recruit NKT cells and play a role in the initial stage of granulomatous reactions (non-patent references 4 and 5). The biosynthetic relationships among phosphatidyl inositol (PI), PIMs, LM and LAM have recently been evidenced by biochemical (non-patent references 6 and 7) and genetic (non-patent references 8 and 9) studies; however, details of this pathway remain highly deductive. However, the structures of LAM from many species, including Mycobacterium tuberculosis, Mycobacterium leprae, Mycobacterium bovis BCG, and Mycobacterium smegmatis, have been widely described in the past 10 years. LAM is a complex glycolipid composed of D-mannan and D-arabinan attached to the PI portion that anchors to the glycolipid in the mycobacterial cell wall (non-patent reference 10).
In LAM molecules, three kinds of capping motifs are known. The first is ManLAM, which has a mannosyl cap, isolated from M. tuberculosis, Mycobacterium kansasii and the like; the second is PILAM, which has a phosphatidyl inositol cap, isolated from M. smegmatis and the like; the third is AraLAM, which has no capping motif, isolated and purified from M. chelonae and the like.
ManLAM contributes to the persistence of mycobacteria that accumulate and grow slowly in the human body. The anti-inflammatory activity of ManLAM has been shown to require an interaction of ManLAM with mannose receptor and/or dendritic cell-specific ICAM-3 (intracellular adhesion molecule-3) grabbing non-integrin via mannose cap motifs (non-patent references 11, 12, and 13). Conversely, PILAM is capable of inducing the release of a wide variety of pro-inflammatory cytokines via activation of Toll-like receptors 2 (TLR-2) (non-patent references 14, 15, and 16). Because AraLAM exhibits no activity, this activity seems to require PI caps (non-patent reference 17). LM has been shown to activate macrophages in a TLR-2-dependent and TLR-4- and TLR-6-independent manner (non-patent references 18, 19, and 20). Therefore, the ManLAM/LM balance may be a parameter that influences the net immunoreactions against mycobacteria.
IL-12 is known to be capable of enhancing anti-tumor immunity, and suppressing Th2-related diseases such as allergic diseases, by promoting the differentiation of naive CD4T cells into Th1 cells (IFNγ-producing cells), and inhibiting the differentiation into Th2 (IL-4-producing cells) Some findings have been reported regarding these effects of LAM and LM on IL-12 production.
It is stated in non-patent reference 21 that BCG infections and the addition of Mannose-capped lipoarabinomannan (ManLAM) in the process of the differentiation from human monocytes to dendritic cells reduce subsequent IL-12 synthesis in dendritic cells, and that IL-12 p35 and p40 mRNA synthesis was more potently suppressed by ManLAM than by AraLAM.
It is stated in non-patent reference 11 that the ManLAMs derived from Mycobacterium bovis BCG and Mycobacterium tuberculosis dose-dependently suppressed LPS-induced IL-12 production by human dendritic cells, and that this inhibitory activity was lost by deleting the Mannose cap or GPI acyl residues.
It is stated in non-patent reference 22 that the AraLAM derived from a Mycobacterium sp. is capable of inducing IL-12 expression in mouse macrophages (J774 cell lines, intraperitoneal macrophages), whereas the ManLAM derived from the Erdman strain is incapable of inducing IL-12 expression.
It is stated in non-patent document 20 that irrespective of the kind of Mycobacterium, ManLAM did not induce the expression of the IL-12 gene in mouse macrophages (RAW264.7, marrow-derived macrophages), whereas PILAM induced IL-12 secretion, that non-capped LAM purified from Mycobacterium chelonae did not induce IL-12 secretion, and that LM potently induced IL-12 irrespective of the kind of Mycobacterium. 
According to these findings, LAM induces IL-12 production by mouse macrophages but suppressively acts on IL-12 production by human macrophages.
The dendritic cells (DC) patrol peripheral tissues as sentinels for the immune system, and are critically important to the induction of cellular immunity against intracellular pathogens, including mycobacteria (non-patent reference 23). Much evidence has demonstrated that DCs are the major APC for the initiation of primary T cell responses as well as the initial source of IL-12 in mycobacterial infections (non-patent references 24, 25, and 26). Infections of Mycobacterium tuberculosis and M. bovis bacillus Calmette-Guerin (BCG) to human or mouse myeloid DC induce a well balanced process of cell maturation and up-regulation of IL-12 production (non-patent references 27 and 28). When BCG-infected DCs are transferred to mice, rapid IFNγ responses against the mycobacterial antigens occur (non-patent reference 27), and DCs infected with M. tuberculosis induce potent immunity against experimental tuberculosis in mice (non-patent reference 29).
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